The multiplexers or demultiplexers, also called OMUX (output multiplexer) notably incorporated in space equipment are subject to significant temperature variations. These OMUX generally include a number of channels linked together by at least one waveguide, also called manifold, the dimensional variations of which, due to the temperature variations, induce an offset of the geometrical distance between the OMUX channel connection ports and phase shifts in the guided waves. These phase shifts lead to a malfunction of the equipment and can, for example, cause OMUX channel mismatches.
To overcome this problem, it is known to produce the waveguide in a material with low coefficient of thermal expansion CTE, such as titanium or an alloy of iron and nickel such as, for example, Invar (registered trademark). However, since space equipment is generally produced in low density materials such as aluminum which has a high coefficient of thermal expansion, assemblies with waveguides with low CTE cause, during temperature variations, significant mechanical stresses between the structures that might lead to malfunctions.
The document U.S. Pat. No. 5,428,323 describes a method of compensating for the thermal expansion of a rectangular-section waveguide by applying a deformation to its two narrower lateral walls so as to ensure phase stability. The deformation is applied by distancing pieces orthogonal to the small sides and fixed between the small sides of the waveguide and a securing structure with low CTE arranged around the waveguide. In the event of a temperature variation, the distancing pieces are elongated or retracted and pull or press orthogonally on the small sides, which forces the small sides of the waveguide to be deformed along an axis orthogonal to these small sides. However, this technology requires the use of a securing structure arranged around the waveguide.
The document EP 1 909 355 describes another waveguide assembly with phase stability in which lever mechanisms are actuated rotation-wise around pivots under the action of temperature variations and make it possible to compensate for greater dimensional variations of the waveguide according to the temperature by pulling or pressing orthogonally on the small sides of the waveguide. However, this assembly is complex, bulky and may hamper the positioning of the adjacent channels and of the mechanical interfaces of the OMUX in proximity to the waveguide, particularly in the context of a compact herringbone configuration according to which the channels are arranged in a zigzag either side of the waveguide.
The document CA 2 432 876 describes another waveguide assembly with phase stability in which the small sides of the waveguide have an initial curved length and are constrained in a lateral direction of the waveguide by a plurality of plates with low CTE placed side by side along the waveguide laterally on either side of each small curved side. The expansion or contraction of the small sides is restricted by the lateral plates whereas the large sides are free to expand or contract. This assembly has the drawback of requiring the small side of the waveguide to be pre-curved while laterally and symmetrically ribbing the top and bottom parts of the waveguide, thus reducing the margin for positioning the channels relative to the waveguide and the mechanical interfaces of the OMUX in proximity to the waveguide.